The insufficient delivery of oxygen to cells and tissues is associated with anemia, which is defined as a deficiency in the blood's oxygen-carrying capacity, and ischemia, in which restrictions in blood supply are caused by a constriction or blockage of blood vessels. Anemia can be caused by the loss of red blood cells (hemorrhage), excessive red blood cell destruction (hemolysis) or deficiencies in erythropoiesis (production of red blood cells from precursors found in the bone marrow). The symptoms of anemia can include weakness, dizziness, fatigue, pallor, impairment of cognitive function and a general reduction in quality of life. Chronic and/or severe anemia can lead to the exacerbation of myocardial, cerebral or peripheral ischemia and to heart failure. Ischemia is defined as an absolute or relative shortage of oxygen to a tissue or organ and can result from disorders such as atherosclerosis, diabetes, thromboembolisms, hypotension, etc. The heart, brain and kidney are especially sensitive to ischemic stress caused by low blood supply.
The primary pharmacological treatment for anemia is administration of some variant of recombinant human erythropoietin (EPO). For anemias associated with kidney disease, chemotherapy-induced anemia, anemia from HIV-therapy or anemia due to blood loss, recombinant EPO is administered to enhance the supply of the hormone, correct the shortage of red blood cells and increase the blood's oxygen-carrying capacity. EPO replacement is not always sufficient to stimulate optimal erythropoiesis (e.g., in patients with iron processing deficiencies) and has associated risks.
Hypoxia-inducible factor (HIF) has been identified as a primary regulator of the cellular response to low oxygen. HIF is a heterodimeric gene transcription factor consisting of a highly regulated α-subunit (HIF-α) and a constitutively expressed β-subunit (HIF-β, also known as ARNT, or aryl hydrocarbon receptor nuclear transporter). HIF target genes are reported to be associated with various aspects of erythropoiesis (e.g., erythropoietin (EPO) and EPO receptor), glycolysis and angiogenesis (e.g., vascular endothelial growth factor (VEGF)). Genes for proteins involved in iron absorption, transport and utilization as well as heme synthesis are also targets of HIF.
Under normal oxygenation, HIF-α is a substrate in a reaction with molecular oxygen, which is catalyzed by a family of iron(II)-, 2-ketoglutarate- and ascorbate-dependent dioxygenase enzymes called PHD-1 (EGLN2), or egg laying abnormal 9 homolog 2, PHD2 (EGLN1), and PHD3 (EGLN3). Proline residues of HIF-α are hydroxylated (e.g., Pro-402 and Pro-564 of HIF-1α) and the resulting product is a target of the tumor suppressor protein von-Hippel Lindau, a component of an E3 ubiquitin ligase multiprotein complex involved in protein ubiquitination. Under low oxygenation, the HIF-α hydroxylation reaction is less efficient and HIF-α is available to dimerize with HIF-β. HIF dimers are translocated to the cell nucleus where they bind to a hypoxia-responsive enhancer element of HIF target genes.
Cellular levels of HIF are known to increase under conditions of hypoxia and after exposure to hypoxia mimetic agents. The latter includes, but is not limited to, specific metal ions (e.g., cobalt, nickel, manganese), iron chelators (e.g., desferrioxamine) and analogs of 2-ketoglurate (e.g., N-oxalyl glycine). The compounds of the present invention inhibit the HIF prolyl hydroxylases (PHD-1, PHD-2, PHD-3) and can also serve to modulate HIF levels. These compounds therefore have utility for the treatment and/or prevention of disorders or conditions where HIF modulation is desirable, such as anemia and ischemia. As an alternative to recombinant erythropoietin therapy, the compounds of the present invention provide a simpler and broader method for the management of anemia.